Washington — Search engine giant Google Inc. said Thursday that it has begun testing prototype driverless cars on city streets in California.

The vehicles went out on the road Tuesday.

But the company said that even though the prototypes are meant to be fully autonomous — and not have steering wheels or pedals — the prototypes will have the driving devices.

"These prototype vehicles are designed from the ground up to be fully self-driving. They're ultimately designed to work without a steering wheel or pedals, but during this phase of our project we'll have safety drivers aboard with a removable steering wheel, accelerator pedal, and brake pedal that allow them to take over driving if needed," Google said in a blog post Thursday. "The prototypes' speed is capped at a neighborhood-friendly 25 mph, and they'll drive using the same software that our existing Lexus vehicles use — the same fleet that has self-driven over 1 million miles since we started the project."

The fleet has added about 300,000 miles since January.

Google said it has been working with a number of auto suppliers on its fleet of prototype self-driving cars. Google said it worked with Roush, RCO, ZF Lenksysteme, Continental, Bosch, Frimo, LG Electronics, Prefix and others to build about 150 fully autonomous vehicle prototypes — with Roush assembling them in Livonia. The company has been in talks with numerous automakers about potentially building a future autonomous vehicle.

So far, the company has reported a handful of crashes to state regulators — mostly being rear ended by other drivers.

Chris Urmson, director of Google's self-driving car project, said in January that the company planned to test a fleet of prototype fully autonomous vehicles without a steering wheel later this year.

He didn't disclose at the time that when tested it would include a steering wheel and pedals for a person sitting in the driver's seat to take over in the event of an emergency.

Urmson said in January he believed it was legal in some states for Google to test autonomous cars that don't have a steering wheel or brakes on U.S. roads. "We don't actually think there is a regulatory block," he said.

Because the cars are low speed — and are not allowed to travel more than 25 mph — they face less restrictive U.S. requirements than full fledged cars. Urmson said in January the test fleet will travel "at lower speeds to reduce the risk when something should go wrong."

NHTSA enacted special rules nearly two decades ago for passenger-carrying low-speed vehicles and neighborhood electric vehicles that go up to 25 mph that aren't required to meet all federal auto safety requirements.

Google says it has built 25 driverless cars to date and still plans to build a total of 150. Initially there are just a few on the road, the company said Thursday.

Asked if Americans will accept self-driving cars that make some mistakes, Urmson said it was a difficult question. "I think there will be failures of these vehicles," Urmson said. "We accept today 33,000 people killed on the roads, but obviously there is challenging perception around risk."

Driverless cars use video cameras, radar sensors, laser rangefinders and detailed maps to monitor road and driving conditions. Automated systems make corrections to keep the car in the lane, brake and accelerate to avoid accidents, and navigate.